Is Heat-On chemically resistant? Anodised Heat-On blocks are resistant to the majority of solvents and splash resistant to dilute acids and alkalis at room temperature. The fluoropolymer coated Heat-On blocks offer superior resistant to the majority of solvents, acids and alkalis. However, it is important to clean off any chemical spills as soon as possible. Be careful that there is not chemical spillage between the flask and the Heat-On. Extended exposure to acids or alkalis will attack the surface of the Heat-On blocks. The stronger the concentration and the longer the exposure time the higher the likelihood of damage and the greater the degree of any damage. Heat will also speed up and intensify any attack.